This invention relates to passenger vehicle suspension systems, and more particularly it relates to an improved configuration for a MacPherson strut that includes a guard structure adapted to prevent damage that may result when the spring used in such a strut becomes broken.
MacPherson struts have become standard components of passenger vehicle suspensions. The use of MacPherson struts has become more prevalent due to the increased popularity of front wheel drive passenger vehicles, since MacPherson strut configurations are the most common form of suspensions for those vehicle drives. In vehicle suspensions, MacPherson struts commonly locate the front drive axle and serve as the vertical axis for the vehicles wheel assembly. Each MacPherson strut normally includes a piston surrounded by a coil spring. The piston is the suspension's damping element for reducing the oscillatory movement of the wheel. The coil spring is supported on the body (or cylinder) of the piston, and acts to cushion the vehicle body from shocks encountered by the wheel. Together, each piston and coil spring supports approximately 30 to 35 percent of the vehicle body weight and are two of the principle support components for the vehicle body.
The MacPherson strut arrangement necessarily places each piston rod and coil spring assembly in close proximity to the vehicle's wheels. Additionally, the brakelines of passenger vehicles using MacPherson struts are often mounted on a bracket that is attached to the MacPherson strut. Consequently, the brakelines are also close to the strut's coil spring and piston. That proximity of the wheel and brakelines to the strut can lead to safety hazards in the event of a failure of the strut's spring. If, for example, a worn, defective, or overstressed coil spring fractures while the vehicle is operating, the fractured spring in conventional MacPherson strut configurations can contact the vehicle's tire. If the contact is with a sharply broken end of the spring, it can either wear the tire or even cause the fractured spring to tear into and puncture the tire. Similarly, a fractured coil spring can tear or sever a vehicle brakeline, resulting in unexpected loss of at least some braking ability. While most modern vehicles have separate front and rear hydraulic brakes systems so that total braking ability will not be lost, such a spring fracture could nevertheless produce a control problem since the brake failure would probably be combined with an unexpected loss of suspension support and loss of full vehicle control.
The spring fracture problems in conventional struts are compounded by the frequent use of coil springs that have multiple diameters. For example, MacPherson strut springs commonly include both a lesser diameter portion and a greater diameter portion, with a continuous change between diameters. The different diameters produce variable spring constants, and consequently cause the suspension to provide different amounts of support at differing strut loads. Conventionally, the smaller diameter portion of the spring is located at the spring's bottom. It is usually attached to the strut by resting on a relatively small diameter spring seat that is constructed of a disk mounted around the strut's cylinder. When spring fracture occurs, the larger diameter portion of the spring is often of a diameter larger than the spring seat, so that the larger diameter coils of the spring can fall beneath the spring seat to a position around the lower portion of the strut. Since passenger vehicle brakelines are conventionally mounted on the strut near the strut's bottom, the probability of brakeline damage upon spring failure is greater when such variable diameter springs are used.
Regardless of the diameter of the spring, and regardless of the size of the spring seat, a fractured spring can often still move to the lower portion of the MacPherson strut by "corkscrewing" around that strut and winding downward to beneath the spring seat. Again, the fractured spring then produces a hazard not only to the wheel's tire but to the vehicle's front braklines as well, with potentially dangerous damage resulting.